Grinder pumps are commonly used in liquid transfer applications that require the grinding of large solid or semisolid materials contained in a liquid, in order to grind, cut, or shred such materials. Ultimately, such solid or semisolid materials are reduced in size to the point where a slurry is formed, which is more easily pumped or otherwise transported, and which is more disposable than the solids themselves. Grinder pumps typically have an axial inlet connected to a pumping chamber, and a driven shaft extending through the pumping chamber and into the inlet. The shaft rotates a cutting cylinder in proximity to an annular ring, or a cutting disk in proximity to a plate cutter, thereby effecting the cutting action of the pump. Numerous other variations and configurations of grinder pumps are known, which are intended to provide shearing action between shearing parts operating cooperatively at close tolerances.
A number of patents have disclosed such grinder pumps, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 3,650,081 of Conery et al. discloses a grinder pump including an electric motor drive, a cooperating cutter blade, and grinder members, one of which is secured to the motor shaft at an inlet for the unit.
U.S. Pat. No. 3,961,758 of Morgan discloses a submersible pump for pumping liquids and liquid slurries, and for concurrently grinding and comminuting solid and semi-solid material contained in the liquid product to be pumped. The liquid product is initially shredded by a cutter bar and then drawn upwardly through a grinding and comminuting section where an abrasive drum mounted on a rotary drive shaft cooperates with an interior cylindrical stator surface to grind and comminute solids and semi-solids contained in the liquid product. From the grinding section, the resulting slurry is drawn into a centrifugal pump section with an impeller having a frusto-conical pumping face formed with symmetrical pumping cavities that are operable in both directions of rotation.
U.S. Pat. No. 4,108,386 of Conery et al. discloses a grinding pump including a comminutor located at the pump inlet to grind solid material as it passes therethrough and into a pumping chamber. The comminutor includes a stationary annular ring in the inlet having a plurality of grinding teeth which form the internal diameter of the ring. A cutting impeller is rotatable within the ring and has at least one blade which extends from one side of the impeller body axially outwardly beyond the ring to force the material between the teeth of the ring. The other side of the impeller body is provided with means to provide additional shearing of the material and prevent clogging of the material between the teeth of the ring.
U.S. Pat. No. 4,378,093 of Keener discloses a grinder pump cutter assembly specifically adapted to be useful in grinding rubber and other elastomeric substances. The grinder pump cutter assembly comprises a pair of cutting blades mounted on a cutter disk which extend at a hook angle to substantially the center of the disk, and a blade that is multi-surfaced, with the surfaces thereof being angled toward the periphery of the disk to break up centralized matter and disperse it into cutting engagement between the disk and a cutter ring.
U.S. Pat. No. 4,454,993 of Shibata et al., discloses a grinder pump which includes a motor driven impeller, a grinder ring fitted in the suction port at the bottom of a pump casing, the grinder ring being provided with a plurality of axially extending grinding grooves and edges on the inner surface thereof, and a grinder impeller fixedly screwed on the distal end of the pump shaft, the grinder impeller being provided with at least two axially extending grinding blades provided on the lower conical surface of the hub thereof so that any foreign material contained in the pumping liquid is ground or shredded into smaller pieces by cooperation of the grinding edges of the grinder ring with the grinding blades of the grinder impeller.
U.S. Pat. No. 4,640,666 of Sodergard discloses a grinder pump comprising a pump housing having an internal surface bounding a central inlet and provided with grooves and an impeller having at least a portion received in the inlet for rotation therein, the portion being substantially cylindrical and having a diameter which is smaller than that of the inlet, the portion having substantially axially extending cutting means which project radially from the portion to cooperate with the grooves to cut solid objects such as rags and other elongated objects.
U.S. Pat. No. 4,697,746 of Nishimori discloses a release type grinder pump that is capable of readily permitting the fitting and removal of a grinder ring with respect to a pump casing. The grinder pump includes an annular suction cover in which the grinder ring is fittedly held and which is detachably fitted in the pump casing so as to surround a suction port and allow the grinder ring not to have any portion directly held within the pump casing.
U.S. Pat. No. 4,842,479 of Dorsch discloses a high head centrifugal slicing slurry pump comprising a booster propeller that is located at the inlet of a flared funnel leading toward arcuate inlet apertures in an end plate of a centrifugal pump casing. The propeller has radially projecting blades of generally right triangular cross section with bases formed of the broad trailing sides and broad bottom sides remote from an impeller; the hypotenuse side of each blade being a broad upper surface inclined relative to a plane perpendicular to the axis for propelling slurry toward the inlet apertures of the pump.
U.S. Pat. No. 5,016,825 of Carpenter discloses a cutting assembly for a grinder pump comprising a disk member rotatable within an opposing annular ring. The inner circumferential surface of the annular ring carries a plurality of cutting teeth, which partially extend at an angle along the lateral dimension of the inner circumferential surface. The disk member has an annular edge which separates a side distal to the pump inlet and a side proximal to the inlet. At least one projection extends from the distal side and has a leading edge facing toward the direction of normal shaft rotation. At least one cutting member extends from the proximal side and also has a leading edge. The proximal side has a recess forming first and second cutting edges. Similarly, the distal side has a recess having first and second cutting edges. The proximal recess overlaps the distal recess along the width of the annular edge.
U.S. Pat. No. 5,044,566 of Mitsch discloses a grinder pump comprised of a housing; a shaft disposed within the housing, a moveable cutter carried on and rotationally coupled to the shaft. A stationary cutter is held within the housing and the moveable cutter cooperates with the stationary cutter to perform cutting along respective surfaces of the moveable cutter and the stationary cutter. The respective surfaces of the stationary and moveable cutters are substantially within a plane that is substantially perpendicular to the axis of the shaft. The pump includes an apparatus that resiliently biases the moveable cutter against the stationary cutter.
U.S. Pat. No. 5,256,032 of Dorsch discloses a centrifugal chopper pump comprising open impeller with vanes having cutting edges at both the intake side of the pump bowl and the closed side of the bowl. The cutting edges of the vanes cooperate with narrow anvil ribs projecting inward from both sides of the pump bowl such that solid matter in the material being pumped is sliced and chopped inside the bowl.
U.S. Pat. No. 6,010,086 of Earle et al. discloses a grinder pump comprised of a pump assembly, a grinder mechanism, and a motor disposed between the grinder mechanism and the pump assembly. A shaft of the motor is operably attached at one end thereof to the grinder mechanism and at the other end thereof to the pump assembly to provide small radial clearances between the cutting portions of the grinder mechanism. In one embodiment, vortex-type impeller vanes are associated with a grinding head of the grinder mechanism to assist flow of effluent from the grinder mechanism to the pump assembly via a passageway extending about, and/or in parallel with, a motor mounting unit.
U.S. Pat. No. 6,190,121 of Hayward et al. discloses a centrifugal pump with solids cutting capability comprising an impeller having a plurality of radially extending vanes connected to a hub and a partial back shroud with sharpened leading edges. The pump has a pump casing with a back plate adjacent to the back side of the impeller, wherein spiral grooves on the back plate interact with the sharpened edges on the back shroud to aid in protecting the area between the back plate and the impeller by cutting of solids and expulsion of solids through an output port. The leading edges on the back shroud are preferably also serrated and beveled and the spiral grooves are outward threaded. A disintegrator is preferably mounted on the end of the drive shaft in the conical intake of the pump. Cutting bars on the front plate of the casing project into the pump intake and interact with front edges of the vanes to cut incoming solids in a liquid mixture.
The disclosures of each of these United States patents are incorporated herein by reference.
Also known is the Shark® 820 grinder pump manufactured and sold by the Zoeller Co. of Louisville, Ky. This pump is comprised of a star-shaped cutter rotating against a stationary flat disc having inlet apertures, with radial grooves disposed between such apertures.
Also known is the Piranha® Grinder pump manufactured and sold by the ABS Corporation. This pump is comprised of an intake plate having spiral cutting grooves on the inside thereof cooperating with the edges of the pump impeller vanes, which are flat in profile. The cutter design of this pump is susceptible to binding problems because material is cut in large pieces and such material can become wedged either in the cutter or between the impeller edges and the intake spiral cutting plate. Also the discharge of this pump can become clogged under severe operating conditions.
It is known that that the configuration of the cutting disk and annular ring, or of the other shearing parts are of high importance in the operation of grinder pumps. The particular shearing parts must be capable of shearing a wide range of entrained solids in a liquid stream that is entering the pump. Such solids may have a wide variety of properties that are adverse to the operation of the pump, including high shear strength, abrasiveness, hardness, elasticity, and/or plasticity. Materials that are abrasive may gradually wear away the cutting edges of the grinding parts of the pump. Materials that have high shear strength and/or high hardness may shatter or deform the cutting edges of the grinding parts of the pump. Materials that undergo elastic and/or plastic deformation may be particular resistant to the cutting action by the grinding parts of the pump. Instead of being cleanly cut up into smaller parts, these materials may deform and “gum up” or otherwise clog the grinding pump.
Fibrous, string-like materials suspended in a liquid are particularly difficult to shred with a grinder pump. On a local scale on the order of the fiber diameter, these materials have a relatively small cross section and are more difficult to shear by the cutting edges. In addition, the relatively long length and elastic or plastic properties often cause them to wrap around the internal pump components parts such as a cutting disk, an annular ring and a pump shaft. It is therefore desirable that the grinding parts of a grinder pump are not only capable of efficient grinding/cutting of solids or semisolid materials, such as e.g. materials in a sewage stream, but also have the capability of grinding fibers and string-like materials that are suspended in such a stream. It is also desirable that the grinder pump be capable of rejecting any very hard objects that are not grindable, such as metal buttons, rivets and the like that may be on objects such as clothing items that are accidentally introduced into the stream. Numerous prior art grinder pumps are not capable of rejecting such hard objects, rendering them especially vulnerable to jamming at start up.
In addition, numerous prior art grinder pumps are not capable of grinding a sudden heavy load of fibrous material that may be encountered. Such grinder pumps will bog down and clog on the heavy fibrous load, or suddenly jam if a hard solid object is introduced into the cutting parts of the pump. The applicant's grinder pump comprised of his cutter assembly invention is capable of rejecting hard objects, and grinding a sudden heavy load of fibrous material. The applicant's grinder pump is also capable of grinding suspended solids into a sufficiently small size so as to produce a substantially homogeneous liquid. The applicant believes that such a capability enables his grinder pump to pump such a liquid at a higher pressure through a smaller diameter pipe. Because of these capabilities, the applicant's grinder pump including his cutter assembly invention is thus superior to prior art grinder pumps. Accordingly, embodiments of the present invention are provided that meet at least one or more of the following objects of the present invention.
It is an object of this invention to provide a grinder pump with a cutter assembly that is capable of grinding a sudden heavy load of solid fibrous material without stalling, or without becoming clogged and ceasing the pumping of liquid therethrough.
It is a further object of this invention to provide a grinder pump with a cutter assembly that is capable of grinding a substantial and continuous load of solid and semisolid material, including fibrous material, without stalling, or without becoming clogged and ceasing the pumping of liquid therethrough.
It is another object of this invention to provide a grinder pump with a cutter assembly that is capable of rejecting a piece of hard solid material, thereby preventing such material from jamming and stalling such pump, and ceasing the pumping of liquid therethrough.
It is a further object of this invention to provide a grinder pump comprised of a cutter assembly that renders such pump capable of pumping a homogenized liquid stream at a higher pressure and through a smaller diameter pipe.